1. Technical Field
The present invention relates to an ink for inkjet recording, an ink cartridge, an inkjet recording method, an inkjet recorder, an ink-recorded matter and a method of producing the ink-recorded matter using the ink.
2. Description of the Related Art
Recently, inkjet recording methods have been popular as image forming methods because of having advantages of having simpler process and easier full-colorization than the other recording methods, and producing high-resolution images even with an apparatus having simple composition. The inkjet recording methods have a small amount of ink soar and adhere to recording media such as papers to form images thereon with an inkjet recorder, and applications thereof are expanding, e.g., personal and industrial printers and printings.
In the inkjet recorder, an aqueous ink using a water-soluble dye is mostly used as a colorant. However, the ink has disadvantages of having poor weatherability and water resistance. Therefore, a pigment ink using a pigment instead of the water-soluble dye has been studied recently. However, the pigment ink is still inferior to the dye ink in colorability, ink discharge stability and preservation stability. In company with improvement of higher-quality image technology of OA printers, even when recorded on plain papers as recording media with the pigment ink, image density equivalent to that of the dye ink is required. However, the pigment ink penetrates into a plain paper as a recording medium and pigment density at the surface of the paper lowers, resulting in lower image density. In order to dry the ink adhering to the recording medium quicker to print quicker, a penetrant is added to the ink for water to penetrate into the recording medium. Then, not only water but also pigment penetrates deeper into the recording medium, resulting in lower image density.
Various methods are disclosed to improve image density. For example, Japanese published unexamined application No. JP-2011-122072-A discloses an ink used for recording on a paper including a water-soluble multivalent metal salt. The ink includes (a) a pigment and (b) at least one compound having no surface activating ability, a molecular weight of from 150 to 10,000, and a content rate of phosphorous ((p/molecular weight)×100) from a functional group selected from a functional group having a basic skeleton of phosphoric acid and functional group having a basic skeleton of phosphonic acid not less than 1.4. Further, the ink includes the (b) compound of from 1.5 to 10.0% by weight.
Japanese published unexamined application No. JP-2007-153985-A discloses an aqueous ink for inkjet recording, essentially including carbon black or an organic pigment, a polymer, a basic material and water. The ink includes a copolymer essentially including a (meth)acrylic acid and other copolymerizable monoethylene unsaturated monomers and a copolymer essentially including monoethylene unsaturated monomers including a phosphoric acid group and other copolymerizable monoethylene unsaturated monomers.
Japanese published unexamined application No. JP-2004-277519-A discloses an inkjet ink including a pigment, a resin having a weight-average molecular weight of from 1,000 to 50,000 and a phosphoric acid group and a solvent having a boiling point not less than 130° C., and a viscosity o from 3 to 15 mPa·s at a temperature of the head when discharging the ink.
However, the ink disclosed in Japanese published unexamined application No. JP-2011-122072-A does not sufficiently improve image density on a plain paper having a low content rate of a water-soluble multivalent metal salt.
The ink disclosed in Japanese published unexamined application No. JP-2007-153985-A does not produce images having sufficient image density when the content of the monoethylene unsaturated monomers including a phosphoric acid group in the copolymer is low. When the content is increased, the carbon black or the organic pigment may unstably be dispersed in the ink.
The ink disclosed in Japanese published unexamined application No. 2004-277519-A is not an aqueous ink and supposed to be used on a film as a recording medium. Improvement of image density on a plain paper by reaction between the metallic ion and the phosphoric acid cannot be expected. Further, since the dispersant stabilizes dispersion of a pigment in a nonaqueous solvent, a pigment may be unstably dispersed in an aqueous ink when the same dispersant is used therein.
Namely, the inks disclosed in Japanese published unexamined applications Nos. JP-2011-122072-A, JP-2007-153985-A and JP-2004-277519-A do not produce images having high image density on a plain paper including no or a low content rate of a water-soluble multivalent metal salt.
Because of these reasons, a need exists for an ink for inkjet recording, which produces images having high image density even on a plain paper including no or a low content rate of a water-soluble multivalent metal salt, and in which a pigment is stably dispersed.